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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109764] V2SI multiply high is not vectorized
 on x86_64
Date: Mon, 08 May 2023 08:09:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109764

--- Comment #3 from Uro=C5=A1 Bizjak <ubizjak at gmail dot com> ---
(In reply to Richard Biener from comment #2)
> Confirmed.  Pattern recog recognizes the widening multiplication but not a
> highpart multiplication.  That's currently missing.

Please note that the following testcase that multiplies short -> int:

--cut here--
#define N 2

unsigned short ur[N], ua[N], ub[N];

void mulh (void)
{
  int i;

  for (i =3D 0; i < N; i++)
    ur[i] =3D ((unsigned int) ua[i] * ub[i]) >> 16;
}

void mulh_slp (void)
{
  ur[0] =3D ((unsigned int) ua[0] * ub[0]) >> 16;
  ur[1] =3D ((unsigned int) ua[1] * ub[1]) >> 16;
}
--cut here--

vectorizes with -O2 -fno-vec-cost-model via .MULH:

  vect__15.6_1 =3D MEM <vector(2) short unsigned int> [(short unsigned int
*)&ua];
  vect__17.9_3 =3D MEM <vector(2) short unsigned int> [(short unsigned int
*)&ub];
  vect_patt_34.10_5 =3D .MULH (vect__15.6_1, vect__17.9_3);
  MEM <vector(2) short unsigned int> [(short unsigned int *)&ur] =3D
vect_patt_34.10_5;

and generates expected:

        movd    ua(%rip), %xmm0
        movd    ub(%rip), %xmm1
        pmulhuw %xmm1, %xmm0
        movd    %xmm0, ur(%rip)

in both cases.=